Bleach questions

[Reide]

I overheard one of my teachers saying:
"Because this hair is darker you will need a minimum of 30vol to colour the hair. It will only process for 40 minutes. After that the bleach stops processing."

Now I was doing some research and stumbled upon a colour theory video where the teacher suggests to use a lower developer to get the maximum lift over a longer period of time while keeping the integrity of the hair. They said a lower developer doesn't blow open the cuticle and the slower process allows you to get a cleaner result.

I was wondering are both ways technically correct? Is one a more of an old fashion way? Does it depend on the products (the stylist kept referring to his product line)?

Both ideas seemed contradicting and since I'm currently in lockdown till the 3rd I thought I would ask for some kind of clarification.

 

[krisko]

Bleach doesn`t stop. It will keep on lifting as long as it is moist.

 

[Reide]

See I did think that. I'm wondering why they are teaching this. I wonder if it's a cautious practice that they are teaching in schools to prevent any severe issues.